[PATCH 46/63] drm/i915: Remove request retirement before each batch

[Chris Wilson]

This reimplements the denial-of-service protection against igt from
commit 227f782e4667 ("drm/i915: Retire requests before creating a new
one") and transfers the stall from before each batch into get_pages().
The issue is that the stall is increasing latency between batches which
is detrimental in some cases (especially coupled with execlists) to
keeping the GPU well fed. Also we have made the observation that retiring
requests can of itself free objects (and requests) and therefore makes
a good first step when shrinking.

v2: Recycle objects prior to i915_gem_object_get_pages()

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h            | 1 -
 drivers/gpu/drm/i915/i915_gem.c            | 7 +++++--
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 2 --
 drivers/gpu/drm/i915/i915_gem_request.c    | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index dcca1078a741..12c6c5b899b2 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3166,7 +3166,6 @@ struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *engine);
 
 void i915_gem_retire_requests(struct drm_i915_private *dev_priv);
-void i915_gem_retire_requests_ring(struct intel_engine_cs *engine);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ea908bed9b03..067bf660cf74 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2244,7 +2244,6 @@ int
 i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 {
 	struct drm_i915_private *dev_priv = to_i915(obj->base.dev);
-	const struct drm_i915_gem_object_ops *ops = obj->ops;
 	int ret;
 
 	if (obj->pages)
@@ -2257,7 +2256,10 @@ i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 
 	BUG_ON(obj->pages_pin_count);
 
-	ret = ops->get_pages(obj);
+	/* Recycle as many active objects as possible first */
+	i915_gem_retire_requests(dev_priv);
+
+	ret = obj->ops->get_pages(obj);
 	if (ret)
 		return ret;
 
@@ -4434,6 +4436,7 @@ i915_gem_cleanup_engines(struct drm_device *dev)
 static void
 init_engine_lists(struct intel_engine_cs *engine)
 {
+	/* Early initialisation so that core GEM works during engine setup */
 	INIT_LIST_HEAD(&engine->request_list);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index ceaff0a0ecbc..6ec888cf6293 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -781,8 +781,6 @@ i915_gem_execbuffer_reserve(struct intel_engine_cs *engine,
 	bool has_fenced_gpu_access = INTEL_GEN(engine->i915) < 4;
 	int retry;
 
-	i915_gem_retire_requests_ring(engine);
-
 	vm = list_first_entry(vmas, struct i915_vma, exec_list)->vm;
 
 	INIT_LIST_HEAD(&ordered_vmas);
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 9cae206d97bb..56d0210abf30 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -718,7 +718,7 @@ complete:
 	return ret;
 }
 
-void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
+static void i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
 {
 	struct drm_i915_gem_request *request, *next;
 
-- 
2.8.1